CH2X Group Research Articles

C–F Bonds as “Frozen” Nucleophiles: Unconsummated SN2 Reactions

In this note, we present a series of rigid molecules that show close enforced interactions between Ar-F moieties and -CH2X groups in a "tetrel bond" configuration similar to a nascent SN2 attack. We explore the spectroscopic, crystallographic, and chemical reactivity consequences of these unusual interactions, including significant through-space spin-spin couplings, short C-F···CH2X distances, and differential SN1 and SN2 reaction pathways. We also reveal experimental evidence of carbon-based tetrel bonds influencing chemical reactivity in solution. Finally, density functional theory (DFT) calculations are employed throughout this study to confirm and illuminate our experimental data.

Cheetah interspecific SCNT followed by embryo aggregation improves in vitro development but not pluripotent gene expression.

The aim of this study was to evaluate the capacity of domestic cat (Dc, Felis silvestris) oocytes to reprogram the nucleus of cheetah (Ch, Acinonyx jubatus) cells by interspecies SCNT (iSCNT), by using embryo aggregation. Dc oocytes were in vitro matured and subjected to zona pellucida free (ZP-free) SCNT or iSCNT, depending on whether the nucleus donor cell was of Dc or Ch respectively. ZP-free reconstructed embryos were then cultured in microwells individually (Dc1X and Ch1X groups) or in couples (Dc2X and Ch2X groups). Embryo aggregation improved in vitro development obtaining 27.4, 47.7, 16.7 and 28.3% of blastocyst rates in the Dc1X, Dc2X, Ch1X and Ch2X groups, respectively (P<0.05). Moreover, aggregation improved the morphological quality of blastocysts from the Dc2X over the Dc1X group. Gene expression analysis revealed that Ch1X and Ch2X blastocysts had significantly lower relative expression of OCT4, CDX2 and NANOG than the Dc1X, Dc2X and IVF control groups. The OCT4, NANOG, SOX2 and CDX2 genes were overexpressed in Dc1X blastocysts, but the relative expression of these four genes decreased in the Dc2X, reaching similar relative levels to those of Dc IVF blastocysts. In conclusion, Ch blastocysts were produced using Dc oocytes, but with lower relative expression of pluripotent and trophoblastic genes, indicating that nuclear reprogramming could be still incomplete. Despite this, embryo aggregation improved the development of Ch and Dc embryos, and normalized Dc gene expression, which suggests that this strategy could improve full-term developmental efficiency of cat and feline iSCNT embryos.

Partial hydration of n-alkyl halides at the water–vapor interface: a molecular simulation study with atmospheric implications

Classical molecular dynamics simulations with a polarizable force field were used to study adsorption of gas-phase alkyl halides to the surface of liquid water and their hydration properties in the interfacial environment. A systematic investigation has been performed for a set of monosubstituted alkyl chlorides, bromides and iodides of the alkyl chain length from one to five carbon atoms (C n H2n+1X, n = 1–5, X = Cl, Br, or I). All alkyl halides readily adsorb to the water surface and exhibit a strong preference for interfacial (partial) hydration. When adsorbed, the alkyl halide molecules reside primarily in the outermost region of the water–vapor interface. The (incomplete) hydration shell of the surface-adsorbed methyl halide species is centered on the methyl end of the molecule, with the halogen atom largely exposed and facing away from water into the gas phase. The maximum hydration of the longer-chain alkyl halides is localized around the α-CH2 group next to the halogen. With an increasing chain length, the alkyl halide molecules align more parallel to the surface. However, ethyl and propyl halides still have the halogen atom rather exposed, pointing almost freely into the gas phase. The behavior of butyl and pentyl halides on the water surface resembles that of alcohols, with the polar region of the CH2X group interacting with water and the rest of the increasingly nonpolar hydrocarbon chain pointing on average away from water. Consequently, the halogen atom becomes more, albeit not fully, hydrated. The propensity of alkyl halides for the water–vapor interface along with the specific character of the partial hydration of the surface-adsorbed alkyl halides and their preferred interfacial orientation is likely to be of importance for heterogeneous chemical processes, involving alkyl halides adsorbed on the surface of aqueous aerosol droplets or ice particles in the atmosphere.

Selective Sorption of Olefins by Halogen-Substituted Macrocation-Polyoxometalate Porous Ionic Crystals

Ionic crystals [Cr3O(OOCCH2X)6(H2O)3]4[α-SiW12O40]·14H2O (X = Cl [Ia], Br [IIa]) are synthesized by complexation of halogen-substituted macrocations with a silicododecatungstate. Compounds Ia and IIa possess analogous one-dimensional winding channels, and the channel walls are composed of oxygen atoms of silicododecatungstates and −CH2X groups of macrocations. Water of crystallization in Ia (IIa) is desorbed by the treatment in vacuo or under a dry N2 or He flow at 298–303 K, and the corresponding guest free phases Ib (IIb) are obtained. Propylene/propane and ethylene/ethane sorption ratios of Ib at 298 K and 100 kPa are 6.1 and 3.6, respectively. The ethylene/ethane sorption ratio of IIb at 298 K and 100 kPa is 2.8. These values are much larger than those of conventional sorbents. In situ13C MAS NMR spectra of ethylene or ethane sorbed in Ib suggest that host–guest interaction for ethylene is larger than that for ethane. DFT calculation and Monte Carlo simulation are carried out to elucidate the nature o...

Highly Stereoselective Synthesis of Aristeromycin Through Dihydroxylation of 4‐Aryl‐1‐azido‐2‐cyclopentenes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Static and dynamic structures of halogenated dimethyl ether radical cations: An EPR and MO study

The EPR spectra of the radical cations of CH3OCH2F and CH3OCH2Cl generated in CF3CCl3 matrices by ionizing radiation at 77 K were fully analyzed with the help of their selectively deuterated compounds. The spectra were analyzed in terms of hyperfine coupling constants (hfcc) to the 1H nuclei in the CH3 and CH2X (X = F, Cl) groups. Based on the EPR results combined with ab initio and DFT MO calculations, the conformation of the cations was determined; the halogen atom preferentially occupies a position in the molecular C–O–C plane which is perpendicular to the unpaired electron orbital of the central oxygen and the C–O–C–Cl framework has a geometry corresponding to a cis conformation. The temperature-dependent EPR spectra for CH3OCH2Cl+ in CF3CCl3 observed between 50 K and 100 K were analyzed in terms of a three-site chemical exchange model among the three protons, caused by CH3 group rotation. The observed activation energy for the rotation, 3.3 ± 0.5 kJ mol−1, is in reasonable agreement with the value calculated for the potential barrier of the rotation.

Reaction Rate Predictions Via Group Additivity. Part 3: Effect of Substituents with CH2as the Mediator

In the first two papers of this series (Sumathi, R.; Carstensen, H.-H.; Green, W. H., Jr. J. Phys. Chem. 2001, 105, 6910. Sumathi, R.; Carstensen, H.-H.; Green, W. H., Jr. J. Phys. Chem. 2001, 105, 8969), a procedure has been developed on the basis of ab initio quantum chemical calculations to express the generic reaction rate in terms of the thermochemical contributions of the reactive moiety (“supergroup”) in the transition structure. The supergroups are derived with the assumption that the contribution from the unreactive moiety to the thermochemistry is given by its group additivity (GA) values. This paper presents the qualitative justification for partitioning the energy of the transition structure into contributions from unreactive and reactive moieties using atoms in molecule (AIM) analysis. The couplings between these moieties, if any, are studied quantitatively using quantum chemical calculations at the CBS-Q level on reactions of the type XCH2CH3 + Y → XCH2CH2• + HY (X = H, CH3, (CH3)2CH, (CH3)3C, F, Cl, NH2, SH, OH, OCH3, OC(O)H, OC(O)CH3, CHO, COCH3, COOH, COOCH3, CHCH2, CCH; Y = H, CH3). The present work thus focuses on the strength and limitations of the GA procedure and explores the effects of varying electronegative and bulky non-next-neighbor substituents, which are separated from the reactive center by a CH2 group, on supergroup values. Both the C−H bond dissociation energies (BDE) and barrier heights to these reactions vary appreciably depending on the non-next-neighbor substituent, X. The preferred conformation around the XCH2- - -CH2(HY) bond in transition structures is largely determined by the effective hyperconjugative interaction between the bonds of the CH2X group and the forming radical center. The effect of X on reaction barriers is subsequently modeled through a multilinear expression that is based on its inductive, steric, and hyperconjugative parameters, suggesting a practical way to accommodate non-next-neighbor effects on generic rate rules predicted using group additivity.

Through-Space Charge and Dipolar Effects in Substituted Ethanes and 1,1,1-Trifluoroethanes

The results of ab initio calculations with the 6-31+G* basis set are reported on over sixty compounds of the type CZ3CH2X (Z = H, F) and on a few longer chain-substituted alkanes. Data for the eclipsed conformations with Z = H and both the staggered and eclipsed conformations with Z = F are presented. The charges on the atoms in these molecules are determined with the Atoms in Molecules (AIM) and Natural Population Analysis (NPA) methods of analysis. The charges on the fluorine atoms in the trifluoroethyl derivatives parallel those of the hydrogen atoms of the ethyl derivatives. A potential gradient model for charge variations is presented. In this model, the magnitude of the charge is dictated by a through-space electrostatic interaction that arises from the charges on the atoms of the CH2X group. The length of the vectors from the atoms in the CH2X group to the bond critical point of the C−Z (Z = H, F) bond and the angle this vector makes with the C−Z bond are critical parameters. The model is tested in...

First example of the solvent effect on absolute conformation of chiral 3,3-disubstituted 1,4-benzodiazepin-2-ones

Chiral 3,3-disubstituted 1,4-benzodiazepin-2-ones (3S)- 7 and (3S)- 8 reveal solvent dependent conformational equilibria. The conformer with absolute P-conformation, with CH 2X (X = p-tosyl, Cl) group in a pseudoaxial (ψa) position and CH 2OAc group in a pseudoequatorial (ψe) position, prevails in nonpolar solvents, as shown by 1H-NMR and CD spectra. For (3S)- 7 only a small shift of the conformational equilibrium in a polar solvent (DMSO) is observed, whereas compound (3S)- 8 inverts to a prevailing M-conformer. The inversion barrier for M P equilibrium is estimated on the bases of TDNMR data. For compounds (3R)- 5 and (3S)- 7, 8 the relative stability of the M P conformers in the ground state is calculated by the MM2 method; comparison of these results with CD and 1H-NMR data reveal that nonpolar solvents invert the relative stability calculated for the two conformers.

UV-Photoelectron, Electron Transmission, and Dissociative Electron Attachment Spectroscopies of Acetone Oximes

The conformation and the electronic structure of several α-heterosubstituted acetone oximes XCH2(CH3)CNOH (X = H (1), F (2), Cl (3), CH3O (4), C2H5S (5), and (CH3)2N (6)) have been determined by means of a multidisciplinary approach based on ultraviolet photoelectron (UP), electron transmission (ET), and dissociative electron attachment (DEA) spectroscopies and fully optimized ab initio 6-31G** and MP2/6-31G** calculations. The vertical ionization energy (IE) and electron affinity (EA) values related to the HOMO (πCN) and LUMO (π*CN) have been determined by the ΔSCF and ΔMP2 (IE only) procedures. The compounds studied prefer an anti (E) configuration between the OH and the CH2X group and a gauche conformation of the C−X bond with respect to the double bond, except 2 and 4 for which a syn (Z) planar structure is nearly degenerate with the E one. The spectral data, coupled with the results of the calculations, indicate that the properties of the acetone oximes are mainly governed by the mixing between the o...

Correlation of Boiling Points with Molecular Structure for Chlorofluoroethanes

Two six-descriptor models, each descriptor derived directly from molecular structure, were fitted to the normal boiling points (Tb) of ethane plus the 52 known chlorofluoroethanes by multiple linear regression (s = 2.6 K, R2 = 0.998). Both models predict Tb values of 351 ± 2 and 366 ± 2 K for unknown 1,1-dichloro-2-fluoroethane and 1,1,1-trichloro-2-fluoroethane, respectively. Several descriptors treat specially the atoms that remain exterior after X atoms in CH2X groups (X = Cl, F) and H atoms in CHX2 groups attach electrostatically to identical groups of adjacent molecules. Electrostatic repulsion between opposing CX bonds reduces Tb by 20−30 K for half of the compounds.

Additive bond-energy scheme with geminal H-H terms Applications to the enthalpies of formation of alkane derivatives

The additive bond-energy scheme with geminal H–H terms, previously applied to hydrocarbons and alkyl radicals, has been extended to aliphatic alcohols, ethers, thiols, thioethers, amines, aldehydes and ketones, halogenoalkanes and alkanenitriles. Apart from C–X (X=O, N, S, Cl, Br, I, CN), X–H (X=O, N, S) and CO terms, it is necessary to introduce an additional C–C term where either carbon atom is attached to an atom of significantly higher electronegativity (O, N, Cl), or to a carbonyl group. It is also necessary to adopt a different geminal H···H term for CH 2 X groups. For alkanols, the anomalous methylene increment can be incorporated by postulating a linear dependence of the H···H term in RCH 2 OH on the chain length. The agreement between calculated and experimental enthalpies of formation is slightly inferior to that obtained by the Allen method, but requires fewer parameters. A number of experimental enthalpies of formation are identified as being worthy of replication.

Estimation of bond dissociation Gibbs energies for carbon–halogen bonds in anion radicals of some aryl halides and substituted benzyl halides

A thermochemical cycle incorporating the standard potential EoRX/RX˙–. of aryl halides and m- and p-substituted benzyl halides RX, the standard potential EoX˙–/X– of the halide ion X– and the bond dissociation Gibbs energy ΔGoBDE(RX) of RX is used to determine the bond dissociation Gibbs energy ΔGoBDE(RX˙–) of the carbon–halogen bond in some anion radicals RX˙–. The values of EoRX/RX˙– are not directly measurable for most benzylic substrates but can be approximated by the standard potentials for the corresponding compounds in which the CH2X group is replaced by an H atom. The calculations are compared with experimental results and similar calculations published recently.

Analyse structurale des dérivés fonctionnels des acides carboxyliques Partie III. Acétate d'éthyle, dérivés α-halogénés

Methylene bending mode analysis of ethyl esters of acetic and haloacetic acids XCH 2CO 2C 2H 5 where X=H( I), F( II), Cl( III),Br ( IV) and I( V) reveals that in the dissolved state (CCl 4) these compounds have conformations induced by rotating motion of the XCH 2 and C 2H 5 groups (( II), ( III) and ( IV)) or by C 2H 5 group rotation exclusively (( I) and ( V)). In the last case, ( I) exists in gauche and anti conformations while ( V) occurs in gauche—gauche and gauche—anti conformations. A theoretical study of compounds ( I), ( II) and ( III) by the PCILO method and Onsager formalism leads to the following conclusion The conformers of ( I) have a dihedral angle (H 3)CC(H 2)OC of 70° (gauche conformer) and 180° (anti conformer). For ( II) and ( III), there are four stable conformers whose dihedral angle ϕ 3=(H 3)CC(H 2)OC and θ=XCCO values are in agreement with C 2H 5 and CH 2X group orientations found in experimental analysis.

Syntheses de Methylpyridines Deuteriees

AbstractPicolines and 2,6‐lutidines partially deuterated on the methyl group or fully deuterated have been prepared with high isotopic purity. Monodeuteration of the methyl group was obtained either by deuterolysis of lithiated derivatives or by reduction of CH2X group with Bu3SnD. Dideuteriomethyl compounds were synthesized by reduction of the corresponding esters with LiAlD4 and conversion of the alcohol to chloromethyl derivatives which were finally reduced by an acetic acid‐zinc mixture. Exchanges with heavy water on platinum yield γ‐picoline‐D7 and 2,6‐lutidine‐D9.

A Charge Transfer Transition in the Near U.V. Spectrum of 1,3-benzodioxole Derivatives

Abstract 1,3-benzodioxole derivatives [figure 1(A, B)] have been much studied for their biological activities.1–12 Nevertheless, apart from our preceding papers13, 14 only few works have been done as concerns their spectroscopic behaviour and their electronic structures.15, 16 All the derivatives which have been studied in our recent works display a -CH2X group [Bzd-CH2X] in para to one of the oxygens of the five membered oxygenated fused ring (X being -H, -OH, -NH2, -NH+ 3, -COCH3 etc…). We want to study here more strongly perturbating substituents with X directly linked to the benzene chromophore [figure 1(C)] [Bzd-X].

Cubic hyperpolarizabilities and local electric field in alkanes and substituted alkanes

Cubic hyperpolarizability of a family of alkanes and substituted alkanes with a general formula CH3–(CH2)n−2CH2X (6 ≤ n ≤ 16 and X = H, Cl, Br, I) was measured by using third-harmonic generation at 1.064 μm. Using an additivity model and Onsager’s formulas for local-field factors, the cubic hyperpolarizabilities of the and –CH2X groups were determined, and the following values were obtained (in 10−37 esu): γCH2 = 6.6, γCH2X = 5.2 (X = H), 9.3 (X = Cl), 18.3 (X = Br), and 41.4 (X = I). For C–X bonds the corresponding values are γC–H = 2, γC–C = 1.2, γC–C = 7.7, γC–Br = 13.6, and γC–H = 30.6. A comparison of the above values with those found for other organic solvents shows the importance of molecular geometry in the additivity model.

Nuclear Quadrupole Coupling Constant and Conformational Studies

A molecular conformation study on three 3-monosubstituted derivatives of propene has been carried out by evaluating the EFG at the site of the halogen nucleus using a semi-empirical LCAO-MO-SCF method. Calculations are performed on several conformers at INDO and CNDO level, using “sp” and “spd” valence basis sets, with Slater type orbitals as the basis functions. The results obtained for various conformers indicate that the nuclear quadrupole coupling constant is practically independent of the orientation of the CH2X group (X = Cl, Br and I) (Figure 1). The mean value of e2 Qqzz/h (averaged over all conformers) in each system matches favourably with the experimental value, despite the severe approximations that are inherent in the semi-empirical theory as well as in its application in the evaluation of the EFG.

The Determination of Substituent Effects by 13C Nuclear Magnetic Resonance Spectrometry. The Effect of Solvent on CH2X Groups

A previous study of the effect of meta- and para-CH2X substituents on the 13C n.m.r. chemical shifts of the α and β side-chain carbons of β- methoxycarbonylstyrenes (methyl cinnamates ) in ethanol has been extended to cover five additional solvents (Me2SO, Me2CO, CDCl3, CCl4 and C6H6). The results support the earlier claim that, for most substituents , the magnitudes of the substituent -induced shifts are proportional to the inductive effect of X. The major contributor to the latter appears to be the field effect generated by the C-X dipole, with the lines of force passing mainly through the molecule. In non-polar solvents, however, there is evidence that lines of force passing directly through the solvent can also influence the shifts in both the meta and para series.

Intramolecular Interactions between a Group Bearing n-Electrons and a CH2–X Where X is an Electronegative Group

Abstract Conformational equilibrium of 9-(2-acyloxyethyl)-1,4-dimethoxytriptycenes in chloroform-d suggests that the stability of the ±sc conformation increases as the electronegativity of the acyl group increases. The results together with other pertinent data are discussed from the stand point that there is an attractive interaction between the acyloxymethyl and the methoxyl groups in proximity. Reflecting its high ionization potential, the chloro group in 1-position showed no stabilization of the ±sc conformation, although mass spectra and some chemical properties indicate that there is an interaction between the chloro group and highly electronegative CH2X group. A possible correlation of these results with the incipient transition state for SN2 reactions is suggested.